Power system reconfiguration with automatic transfer switch

ABSTRACT

Reconfiguring a power system for an electrical load includes establishing a secondary feed to an electrical load that is receiving power from a primary power source. A set of secondary feed lines is coupled between a donor power source and a power input to the electrical load such that the set of secondary feed lines is configured to supply power from the donor power source to the electrical load. An automatic transfer switch is coupled in parallel with the set of secondary feed lines. The electrical load is transferred by the automatic transfer switch from the donor power source to the primary power source for the reconfiguration.

This application is a continuation of U.S. patent application Ser. No.13/666,867, filed Nov. 1, 2012, now U.S. Pat. No. 9,122,466, which ishereby incorporated by reference in its entirety.

BACKGROUND

Organizations such as on-line retailers, Internet service providers,search providers, financial institutions, universities, and othercomputing-intensive organizations often conduct computer operations fromlarge scale computing facilities. Such computing facilities house andaccommodate a large amount of server, network, and computer equipment toprocess, store, and exchange data as needed to carry out anorganization's operations. Typically, a computer room of a computingfacility includes many server racks. Each server rack, in turn, includesmany servers and associated computer equipment.

Because the computer room of a computing facility may contain a largenumber of servers, a large amount of electrical power may be required tooperate the facility. In addition, the electrical power is distributedto a large number of locations spread throughout the computer room(e.g., many racks spaced from one another, and many servers in eachrack). Usually, a facility receives a power feed at a relatively highvoltage. This power feed is stepped down to a lower voltage (e.g.,110V). A network of cabling, bus bars, power connectors, and powerdistribution units, is used to deliver the power at the lower voltage tonumerous specific components in the facility.

Primary power systems for computer systems in operation typically needto be maintained or reconfigured from time to time. Some data centers,for example, have “single threaded” distribution via the electricalpower supply to the floor and/or to the rack, and in which maintenancecan only be performed when the components using power in the datacenter, such as servers, are shut-off. The down-time associated withmaintenance and reconfiguration of primary power systems in a datacenter may result in a significant loss in computing resources. In somecritical systems such as hospital equipment and security systems,down-time may result in significant disruption and, in some cases,adversely affect health and safety.

For safety reasons, the electrical codes and regulations of somecountries may require that a residual current device (such as a groundfault circuit interruption device) be included in circuits supplyingpower to electrical loads in a data center. In some situations, theresidual current devices may trip in unintended ways that are not neededto ensure safety. For example, actions taken to reconfigure power tocomputing systems under live conditions (such as plugging in a secondaryfeed for the computing systems while a primary power source is active)may cause a residual current device to trip, causing an unintended andunnecessary loss of power to the computing systems.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a data center including rack systems that receivepower from a primary power system.

FIG. 2 illustrates connection of a back-feed system from a donor sourcein a floor power distribution unit to a rack power distribution unitthat is supplying power to electrical systems in a rack.

FIG. 3 illustrates a system in which a back feed has been established toa rack power distribution unit supplying power to electrical systems ina rack.

FIG. 4 illustrates an automatic transfer switch connected in parallelwith a back-feed.

FIG. 5 illustrates a system with a system after removal of a back-feedunit and re-connection of cables of a primary power source.

FIG. 6 illustrates a set of electrical systems with primary powerenergized on a normal input of an automatic transfer switch.

FIG. 7 illustrates electrical systems receiving power from primary powersource through an automatic transfer switch.

FIG. 8 illustrates a system that includes a reserve power sourceconnected to an alternate source input of an automatic transfer switch.

FIG. 9 illustrates reconfiguring a power system for an electrical loadin a live setting using an automatic transfer switch.

FIG. 10 illustrates a front panel view of one embodiment of a backfeedcontrol unit.

FIG. 11 is a schematic diagram illustrating input, master control, andoutput portions of a backfeed control unit according to one embodiment.

FIG. 12 is a schematic diagram illustrating supply pre-return checkinlet and load pre-return check socket portions of a backfeed controlunit according to one embodiment.

While the invention is susceptible to various modifications andalternative forms, specific embodiments thereof are shown by way ofexample in the drawings and will herein be described in detail. Itshould be understood, however, that the drawings and detaileddescription thereto are not intended to limit the invention to theparticular form disclosed, but on the contrary, the intention is tocover all modifications, equivalents and alternatives falling within thespirit and scope of the present invention as defined by the appendedclaims. The headings used herein are for organizational purposes onlyand are not meant to be used to limit the scope of the description orthe claims. As used throughout this application, the word “may” is usedin a permissive sense (i.e., meaning having the potential to), ratherthan the mandatory sense (i.e., meaning must). Similarly, the words“include,” “including,” and “includes” mean including, but not limitedto.

DETAILED DESCRIPTION OF EMBODIMENTS

Various embodiments of methods and systems for establishing feeds toelectrical systems, such as computer systems in a data center, aredisclosed. According to one embodiment. According to one embodiment, amethod of reconfiguring a power system for computing devices in a rackincludes establishing a back-feed to computing devices in a rackcomputing system that is receiving power from a primary power source.Establishing the back-feed includes coupling a set of back-feed linesfrom a donor power source to one or more output receptacles of a rackpower distribution unit of the rack computing system such that the setof back-feed lines supplies power from the donor power source to thecomputing devices. An automatic transfer switch is coupled in parallelwith the set of back-feed lines. An alternate source ATS input of theautomatic transfer switch is coupled to the donor power source. An ATSoutput of the automatic transfer switch is coupled to a power input ofthe computing devices such that the computing devices receive power fromthe donor power source via the automatic transfer switch. The set ofback-feed lines is disabled from the computing devices. A normal ATSinput of the automatic transfer switch is coupled to a primary powersource for the reconfiguration. The primary power source for thereconfiguration may be the same as the original primary power source(for example, where the reconfiguration is for cutting in an automatictransfer switch to an existing power system) or different from theoriginal primary power source (for example, for migration from oneprimary power source to another). The computing devices are transferredby the automatic transfer switch from the donor power source to theprimary power source for the reconfiguration.

According to one embodiment, a method of reconfiguring a power systemfor an electrical load includes establishing a secondary feed to anelectrical load that is receiving power from a primary power source.Establishing the secondary feed includes coupling a set of secondaryfeed lines between a donor power source and a power input to theelectrical load such that the set of secondary feed lines is configuredto supply power from the donor power source to the electrical load. Anautomatic transfer switch is coupled in parallel with the set ofsecondary feed lines. An alternate source ATS input of the automatictransfer switch is coupled to the donor power source. An ATS output ofthe automatic transfer switch is coupled to the power input of theelectrical load such that the electrical load receives power from thedonor power source via the automatic transfer switch. The set ofsecondary feed lines is disabled from the electrical load. A normalsource ATS input of the automatic transfer switch is coupled to aprimary power source for the reconfiguration. The electrical load istransferred by the automatic transfer switch from the donor power sourceto the primary power source for the reconfiguration.

According to one embodiment, a system for reconfiguring a power systemfor electrical loads includes a secondary feed system and an automatictransfer switch. The secondary feed system includes a set of secondaryfeed lines that supply power from a donor power source to an electricalload and a feed-switching device that switches power through one or moreof the secondary feed lines. The automatic transfer switch couples inparallel with the secondary feed lines.

As used herein, an “alternate source” means, in the context of anautomatic transfer switch, a source that an automatic transfer switchcan use to supply power to a load when normal conditions do not exist.For example, an automatic transfer switch may switch to an alternatesource input when a normal source fails.

As used herein, a “cable” includes any cable, conduit, or line thatcarries one or more conductors and that is flexible over at least aportion of its length. A cable may include a connector portion, such asa plug, at one or more of its ends.

As used herein, “computer room” means a room of a building in whichcomputer systems, such as rack-mounted servers, are operated.

As used herein, “computing device” includes any of various devices inwhich computing operations can be carried out, such as computer systemsor components thereof. One example of a computing device is arack-mounted server. As used herein, the term computing device is notlimited to just those integrated circuits referred to in the art as acomputer, but broadly refers to a processor, a server, amicrocontroller, a microcomputer, a programmable logic controller (PLC),an application specific integrated circuit, and other programmablecircuits, and these terms are used interchangeably herein. Some examplesof computing devices include e-commerce servers, network devices,telecommunications equipment, medical equipment, electrical powermanagement and control devices, and professional audio equipment(digital, analog, or combinations thereof). In various embodiments,memory may include, but is not limited to, a computer-readable medium,such as a random access memory (RAM). Alternatively, a compact disc-readonly memory (CD-ROM), a magneto-optical disk (MOD), and/or a digitalversatile disc (DVD) may also be used. Also, additional input channelsmay include computer peripherals associated with an operator interfacesuch as a mouse and a keyboard. Alternatively, other computerperipherals may also be used that may include, for example, a scanner.Furthermore, in the some embodiments, additional output channels mayinclude an operator interface monitor and/or a printer.

As used herein, “data center” includes any facility or portion of afacility in which computer operations are carried out. A data center mayinclude servers dedicated to specific functions or serving multiplefunctions. Examples of computer operations include informationprocessing, communications, simulations, and operational control.

As used herein, “floor power distribution unit” refers to a powerdistribution unit that can distribute electrical power to variouscomponents in a computer room. A power distribution unit may be housedin an enclosure, such as a cabinet.

As used herein, a “match”, in the context of matching sets of powerlines, means that the characteristics between the sets of power linesare similar to one another within acceptable limits. A match does notrequire that the measurements of the two items be precisely equal. Insome embodiments, the acceptable variance levels for a match arepredetermined. For example, in one embodiment, for a voltage levelmatch, an input power line may be predetermined to match a feed line ifthe difference in measured voltage between the two lines is 7 volts orless. Various characteristics, such as voltage, waveform, etc. may beused as criteria to determine a match.

As used herein, a “normal source” means, in the context of an automatictransfer switch, a source that an automatic transfer switch can use tosupply power to a load during normal conditions. Normal conditions mayinclude, for example, conditions in which characteristics of the normalsource are measured to be within acceptable limits for the load.

As used herein, “power distribution unit” means any device, module,component, or combination thereof, that can be used to distributeelectrical power. The elements of a power distribution unit may beembodied within a single component or assembly (such as a transformerand a rack power distribution unit housed in a common enclosure), or maybe distributed among two or more components or assemblies (such as atransformer and a rack power distribution unit each housed in separateenclosure, and associated cables, etc.). A power distribution unit mayinclude a transformer, power monitoring, fault detection, isolation.

As used herein, “primary power” means any power that can be supplied toan electrical load, for example, during normal operating conditions.

As used herein, “rack power distribution unit” refers to a powerdistribution unit that can be used to distribute electrical power tovarious components in a rack. A rack power distribution may includevarious components and elements, including wiring, bus bars, connectors,and circuit breakers.

As used herein, “remote power panel” means any panel, device, module,component, or combination thereof, that can be used to transfer ordistribute electrical power from one or more input conductors to one ormore output conductors. In certain embodiments, a remote power panelincludes main lug only (“MLO”) panel conductors. A remote power panelmay be housed in an enclosure, such as a cabinet.

As used herein, “reserve power” means power that can be supplied to anelectrical load upon the failure of, or as a substitute for, primarypower to the load.

As used herein, a “secondary feed” refers to any feed that suppliespower that is separate from a primary power system for at least aportion of a primary power chain.

As used herein, a “tertiary feed” refers to any feed that supplies powerthat is separate from two power systems (such as a primary power systemand a reserve power system) for at least a portion of the two powersystem chains. In some embodiments, a secondary power feed or tertiaryfeed may be completely independent of the primary power distributionsystem. In some embodiments, however, a secondary feed or tertiary feedis not completely independent of the primary power distribution system.For example, both the primary power distribution system and a secondaryfeed may both receive power from the same utility feed, the samestep-down transformer (for example, a primary-side transformer), thesame uninterruptible power supply (for example, a primary-side), etc.

As used herein, “source power” includes power from any source, includingbut not limited to power received from a utility feed. In certainembodiments, “source power” may be received from the output of atransformer.

In some embodiments, a power feed is established to electrical systemswhile systems are live. Systems receiving power from an added feed maybe of various types. Examples include hospital equipment, utilitysystems, security systems, military systems, telecommunications systems,or electronic commerce systems. In certain embodiments, an additionalfeed is provided to a critical system, such as a life support system. Insome embodiments, the systems are computer systems in a data center. Anadditional power feed may allow the primary power system to betemporarily taken off-line for reconfiguration or maintenance of, forexample, the primary power system. In some embodiments, the feed isaccomplished by paralleling a primary power distribution system over aportion of a power distribution chain.

In some embodiments, reconfiguration or maintenance operations areperformed under live conditions (for example, while maintaining serversin a powered up state and performing computing operations using theservers). In one embodiment, computer systems in a rack are maintainedlive while an automatic transfer switch is installed between a floorpower distribution unit and a rack power distribution unit for thecomputer systems. The installed automatic transfer switch may be used,for example, to switch to a reserve power system. The installation maybe carried out in a “live” environment in which the computer systems inthe rack remain in operation.

In some embodiments, reconfiguring a power system for an electrical loadunder live conditions includes allowing an ATS to transfer theelectrical load from a secondary feed to the primary power source forthe reconfigured system. To set up the transfer, the ATS may first beconnected in parallel with the secondary feed to the electrical load.For example, in one embodiment, the ATS is connected in parallel with aback-feed of the secondary power source to a rack PDU supplying power torack-mounted computing devices in a computing room of a data center.

In some cases, a reconfiguration process is used to cut in an ATS so aback-up power source can be added to the system (the back-up powersource may be provided on the alternate input of the ATS). In othercases, the reconfiguration process is used to migrate the computingdevices from one primary power source to another primary power source.

FIGS. 1-8 illustrate cutting in a secondary power source using anautomatic transfer switch to re-establish a primary power source forelectrical systems operating in a data center. The data center may beequipped with a feed device that can feed power to electrical systemsthrough a rack power distribution unit. In one embodiment, the feeddevice taps electrical power from a power source panel and feeds thepower to a rack power distribution unit.

FIG. 1 illustrates a data center having rack systems that receive powerfrom a primary power system. Data center 100 includes rack systems 102and primary power system 104. Rack systems 102 include rack 106 andelectrical systems 108. Electrical systems may include, for example,computer systems, rack-mounted servers, network control devices, powersupply units, air moving devices, and mass storage devices. Primarypower system 104 includes uninterruptible power supply 109 and floorpower distribution unit 110.

In some embodiments, a transformer for each of the power systems iscoupled to a utility feed. The utility feed may be a medium voltagefeed. In certain embodiments, the utility feed is at a voltage of about13.5 kilovolts or 12.8 kilovolts at a frequency of about 60 Hz.Generators may provide power to primary power system 104 in the event ofa failure of utility power to the transformer. In one embodiment, onegenerator provides back-up power for each of two or more primary powersystems. UPS 109 may provide uninterrupted power to rack-mountedelectrical systems in the event of a power failure upstream from UPS109. In certain embodiments, UPS 109 receives three-phase power from atransformer. UPS 109 may supply three-phase power to a floor powerdistribution unit.

Floor power distribution unit 110 may have any number of outputs foreach phase combination. In some embodiments, a floor distribution unitmay have one receptacle for each of the six phase combinations. In someembodiments, a floor distribution unit may have two or more receptaclesfor each of the six phase combinations. In some embodiments, a floorpower distribution may have outputs for only some of the phasecombinations (for example, AB, BC, and AC only). In certain embodiments,a floor distribution unit may receive and/or distribute two-phase power.In certain embodiments, a floor distribution unit may receive and/ordistribute a single phase (for example, hot, neutral, and ground).

Rack systems 102 may be located in a computing room of data center 100.Electrical systems 108 may be coupled to an output receptacle 111 ofrack power distribution unit 112 by way of cables 113. Each of rackpower distribution units 112 may receive power from floor powerdistribution unit 110 by way of one of output panel devices 114. Inoperation of data center 100, any or all of rack PDU receptacles 111 maybe used to supply power to electrical systems in rack system 102, suchas servers.

In one embodiment, rack PDU receptacles 111 are IEC 60320 C13receptacles. In one embodiment, rack PDU receptacles 111 are IEC 60320C19 receptacles. In some embodiments, all of rack PDU receptacles 111are wired in parallel with one another. In other embodiments, rack PDUreceptacles 111 may be split into two or more banks of receptacles. Thereceptacles in each bank may be wired in parallel with one another. Insome embodiments, one bank of receptacles is provided for each hot wirefrom the power source (one bank for A-neutral, another for B-neutral) orfor each hot wire pairing from the power source (AB, BC, AC).

Each of rack power distribution units 112 may be coupled to the poweroutput device 114 in floor power distribution unit 110 by way of primarypower cable 116. Primary power cable 116 is coupled to PDU input cable118 of rack power distribution unit 112. In the embodiment shown in FIG.1, primary power cable 116 is coupled to power output device 114 a.Power output device 114 a includes a circuit breaker (for example, aminiature circuit breaker) and a residual current device (“RCD”). Thecircuit breaker of power output device 114 a may trip based onovercurrent conditions from electrical loads connected to power outputdevice 114 a. The RCD of power output device 114 a may trip as a resultof an imbalance between lines connected to power output device 114 a.(In each of FIGS. 1-8, power transmission for the illustratedconnections is indicated by the arrows.)

Examples of residual current devices that may be used in a powerdistribution unit include residual-current circuit breaker (“RCCB”)devices, residual current circuit breaker with overload protection(“RCBO”) devices, appliance leakage current interrupter (“ALCI”)devices, and ground fault circuit interruption (“GFCI”) devices. Incertain embodiments, a residual current device is used in combinationwith (for example, in series with) one or more circuit breakers.

Automatic transfer switch 120 is provided for establishing a reservepower source for electrical systems 108 of rack systems 102. Initially,automatic transfer switch 120 may be disconnected from rack systems 102.

FIG. 2 illustrates connection of a back-feed system from a donor sourcein a floor power distribution unit to a rack power distribution unitsupplying power to electrical systems in a rack. Back feed system 130may be used to provide a secondary power feed to rack systems 102. Backfeed system 130 includes back feed unit 132, splitter box 134, donorsupply cable 136, back feed unit input cable 138, splitter cable 139,and back feed unit output cables 140 and 142.

Donor supply cable 136 is coupled between floor power distribution unit110 and splitter box 134. Back feed unit input cable 138 is coupledbetween splitter box 134 and back feed unit 132. Back feed unit outputcables 140 and 142 are coupled between back feed unit 132 and outputreceptacles 111 of rack power distribution unit 112.

Donor supply cable 136 is connected to power output device 144. In thisexample, power output device 144 has a circuit breaker, but does notinclude a residual current device. In some embodiments, establishing theback-feed may include replacing a power output device that includes aresidual current device with a power output device that does not includea residual current device. For example, power output device 114 b inposition L1/14 shown in FIG. 1 may include a circuit breaker and aresidual current device. To establish a secondary feed to rack systems102, power output device 114 b may be replaced with a circuitbreaker-only power output device 144.

Once back feed system 130 is connected, a switch may be operated toestablish a back feed. FIG. 3 illustrates a system in which a back feedhas been established to a rack power distribution unit supplying powerto electrical systems in a rack. In some cases, when the switch isclosed in back feed unit 132 to establish the back feed, the residualcurrent device in power output device 114 a of floor power distributionunit 110 trips due to an imbalance in the primary power lines, resultingin the loss of the primary power feed to rack power distribution unit110 (as indicated by the dashed lines in the primary power feed).Nevertheless, electrical systems 108 in rack systems 102 may remainpowered up via the back feed from power output device 144 through backfeed unit 132.

After the back-feed has been established to electrical systems 108, aparallel connection may be established between the back-feed and anautomatic transfer switch. FIG. 4 illustrates an automatic transferswitch connected in parallel with a back-feed.

Automatic transfer switch 120 includes switching unit 150, alternatesource input cable 152, normal source input cable 154, and ATS outputcable 156. (In FIG. 4, the alternate power source input may be referredto as “ATS Source 2” and the normal power source input may be referredto as “ATS Source 1”.) Alternate source input cable 152 is coupled tosplitter cable 139. PDU input cable 118 is disconnected from primarypower cable 116 and connected to ATS output cable 156. Splitter box 134may split donor power from floor power distribution unit 110 between ATSback feed unit input cable 138 and automatic transfer switch 120. Withthis connection in place, electrical systems 108 in rack systems 102 maybe supported by donor power through both back feed unit 132 and thealternate source-side of automatic transfer switch 120.

With the electrical systems supported by both the back-feed system andthe alternate source input to the automatic transfer switch, theback-feed unit may be removed from the system. The normal source inputof the automatic transfer switch may be re-connected to the primarypower source. FIG. 5 illustrates a system with a system after removal ofa back-feed unit and re-connection of cables of a primary power source.Primary power cable 116 may be coupled to normal source input cable 154of automatic transfer switch 120. At this stage, no power may besupplied to automatic transfer switch 120 from primary power cable 116because power output device 114 a on floor power distribution unit 112may be in a disabled condition. For example, a residual current deviceof power output device 114 a may still be in a tripped state from whenthe back-feed was established to rack power distribution unit 112.

With the electrical systems supported by the alternate source input ofthe ATS and the normal source input of the ATS re-connected to theprimary power source, the primary power source may be re-energized tothe ATS normal input. FIG. 6 illustrates a set of electrical systemswith primary power energized on an ATS normal input. Initially, whenprimary power cable 116 may be coupled to normal source input cable 154of automatic transfer switch 120, automatic transfer switch 120 mayremain on the alternate source input side. After power coming intoautomatic transfer switch 120 through normal source input cable 154 hasbeen met predetermined criteria (for example, stable for a predeterminedperiod of time), automatic transfer switch 120 may automatically switchto normal source input cable 154 such that power is supplied toelectrical systems 108 from primary power transmitted through primarypower cable 116. In one embodiment, power is automatically switched byautomatic transfer switch 120 about 5 minutes after the primary powersource is enabled. In some embodiments, primary power to normal sourceinput cable 154 is established by resetting a residual current device inpower output device 114 a of floor power distribution unit 110.

Once the loads of the electrical systems have been transferred to theprimary power source, the back-feed from the donor source may beremoved. FIG. 7 illustrates electrical systems receiving power from aprimary power source through an automatic transfer switch (with nosource on the alternate source input). Electrical systems 108 receivepower from floor power distribution unit 110 by way of primary powercable 116, automatic transfer switch 120, and rack power distributionunit 112.

With the primary power source continuing to supply power to theelectrical system, a reserve power source may be connected the alternatesource input of the ATS. FIG. 8 illustrates a system that includes areserve power source connected to an alternate source input of anautomatic transfer switch. Reserve power system 158 includes floor powerdistribution unit 160, power output device 162, and reserve power cable164. Alternate source input cable 152 may be coupled to reserve powercable 164. Reserve floor power distribution unit 160 may provide reservepower to rack systems 102.

In some embodiments, reserve power system 158 provides reserve power forall of the electrical systems 108 supplied by primary power system 104.In some embodiments, reserve power system 158 is powered up at all timesduring operation of a data center. The reserve power system may bepassive until a failure of one or more components of primary powersystem 104, at which time the reserve power system may become active.

In various embodiments, a secondary feed to a power distribution issupplied by tapping an element in a power chain that is upstream from arack power distribution unit. As illustrated in the embodiments shown inFIGS. 1-8, for example, a back feed to rack power distribution unit 112is supplied from floor power distribution unit 110. Floor powerdistribution unit 110 is upstream from, and supplies power to, rackpower distribution unit 102. In another embodiment, a feed may besupplied from an uninterruptible power supply in the primary powersystem (such as UPS 109 of primary power system 104 shown in FIG. 1). Afeed may, in various embodiments, be supplied from any power source,however. For example, in certain embodiments, a feed may be suppliedfrom a floor power distribution unit in a data center other than thefloor power distribution unit 110, from a reserve power system, or asource external to the data center.

FIG. 9 illustrates reconfiguring a power system for an electrical loadin a live setting using an automatic transfer switch. In someembodiments, a reconfiguration process is used to cut in the ATS so aback-up power source can be added (the back-up power source may beprovided on the alternate input of the ATS) as described above relativeto FIGS. 1-8. In other embodiments, a reconfiguration process is used tomigrate computing devices from one primary power source to anotherprimary power source. For example, in one embodiment, the proceduredescribed above may be modified such that rack systems 102 are coupledto a new primary power source (for example, a different floor powerdistribution unit than floor power distribution unit 110). In someembodiments, the primary power source for the reconfiguration is on thesame phase as the primary power source before the reconfiguration. Inother embodiments, the primary power source for the reconfiguration ison a different phase than the primary power source before thereconfiguration.

At 200, a secondary feed is established for an electrical load that isreceiving power from a primary power source. Establishing the secondaryfeed may include connecting a set of secondary feed lines between adonor power source and a power input to the electrical load such thatthe set of secondary feed lines supplies power from the donor powersource to the electrical load. In some embodiments, a back feed unit isused to switch on the back feed. In one embodiment, a 3-pole breaker isinstalled in a floor PDU to provide a back feed to a rack PDU. Enoughcable may be left exposed on the load side of the breaker to be able tomeasure the current on each phase with a tong ammeter or a grip ammeter.Once installed, the 3-pole breaker may be shut.

At 202, an automatic transfer switch is coupled in parallel with the setof secondary feed lines. An alternate source ATS input of the automatictransfer switch may be connected to the donor power source. The ATSoutput of the automatic transfer switch may be connected to the powerinput of the electrical load. The electrical load may receive power fromthe donor power source via the automatic transfer switch.

At 204, the set of secondary feed lines is disabled from the electricalload. The secondary feed lines may be disabled by operating a switch, orby physically disconnecting cables of the back feed.

At 206, a normal source ATS input of the automatic transfer switch iscoupled to a primary power source for the reconfiguration. In someembodiments, the primary power may be disabled when the normal sourceATS input is connected (for example, a residual circuit device may be ina tripped state). In such cases, an operator may enable primary power(for example, reset the residual current device, or close a switch)after the cables have been connected.

At 208, the electrical load is transferred by the automatic transferswitch from the donor power source to the primary power source for thereconfiguration. The transfer may occur automatically based on aprotocol that is implemented by the automatic transfer switch. Incertain embodiments, a user may input switching criteria for thetransfer to the automatic transfer switch. The criteria may beimplemented by the automatic transfer switch to control switching overto the primary power source. For example, the user may specify stabilitycriteria for power supply for the normal source input that must be metbefore switching from the alternate source input of the automatictransfer switch to the normal source input of the automatic transferswitch. In certain embodiments, switching from the alternate source tothe normal source is controlled by a signal from a system external tothe automatic transfer switch.

In certain embodiments, a reconfiguring a system includes assessingwhether two power sources are matched with one another. For example, foreach PDU, tests may be performed to establish the appropriate phase andwhether a match exists before connecting the input lines to a back feedline for the PDU. In some embodiments, a maximum variation may beestablished for the potential. In one embodiment, the potentials allowedto differ by no more than of 7 VAC. In another embodiment, the potentialis allowed to differ by no more than 5%. In some embodiments, phaseintegrity may be verified by two electricians.

As operations may be performed “hot”, electrical safety precautions maybe utilized, which may include ensuring that: (1) all electrical safetyprocedures are followed; (2) personal protective equipment is used; (3)proper change management/configuration management is in place,identifying the specific rack(s) being back-fed and notifying the properpersonnel; and (4) the primary feed to the server rack(s) has noabnormal conditions that would jeopardize the rack during a secondaryfeed process. For example, power characteristics such as voltagedeviation, frequency deviation, and phase deviation may be determined tobe within acceptable ranges, for example, within plus or minus 5%.Throughout the process, multiple connectors may be energized since anadditional power source is being introduced. Precautions may be takenthat these connectors are carefully handled, and properly insulated.

Equipment for establishing a feed, such as backfeed system 120 describedabove relative to FIG. 1, may be staged in any suitable location. In oneembodiment, the backfeed unit is positioned at the end of row to preventinterference with other server racks. In certain embodiments, testand/or feed equipment may be mounted on a cart.

Although in the examples described above, the secondary feed or backfeedwas established by feeding into a power distribution unit, in certainembodiments, a secondary or tertiary feed may be established by feedinginto other elements in a power distribution system. In certainembodiments, a secondary feed is established by backfeeding into aremote power panel.

Although in the examples described above, a secondary feed is made intoa rack-level PDU, a secondary power feed may in various embodiments besupplied to any component in a system. In one embodiment, a backfeed isestablished into output receptacles of a floor PDU, such as floor powerdistribution unit 110 described above relative to FIG. 1. The powersource may come from any source, such as different floor PDU, a UPS, orother system. A floor PDU back feed may be established, for example, toreplace a circuit breaker in the floor PDU.

FIG. 10 illustrates a front panel view of one embodiment of a backfeedcontrol unit. A backfeed control unit may be used, for example, as aparalleling panel in the backfeed unit described above relative to FIGS.1-8. Backfeed control unit 860 includes front panel 864 and input cable862. Input cable 862 may couple with a power source, either directly orthrough an intermediate system such as a receptacle panel. Mastercontrol 866 and outputs 868 are provided on front panel 864. Mastercontrol 866 includes master switch 870, test points 872, ammeter 874,and indicator lamps 876. Each of outputs 868 includes output receptacle878, test points 880, ammeter 882, and switch 884.

Input cable 862 includes plug 863. In one embodiment, plug 863 is a IEC60309 2P+NE, 32 A plug. In another embodiment, plug 863 is a L6-30Pplug.

Power may be routed from input cable 862 to each of outputs 868. Ammeter874 may provide a visual indicator of a current level in input cable862. Ammeters 882 may provide a visual indication of a current level ineach of outputs 868. Switches 870 and 884 maybe used to control poweroutputs 868.

Backfeed control unit 860 includes supply pre-return check inlet 890 andload pre-return check socket 892. Supply pre-return check inlet 890includes test points 894. Load pre-return check socket 892 includes testpoints 896.

FIG. 11 is a schematic diagram illustrating the input cable 862, mastercontrol 866, and output 868 portions of backfeed control unit 860according to one embodiment. FIG. 12 is a schematic diagram illustratingthe supply pre-return check inlet 890 and load pre-return check socket892 portions of backfeed control unit 860 according to one embodiment.In one embodiment, supply pre-return check inlet 890 is a IEC 603092P+NE, 32 A male connector portion and load pre-return check socket 892is a IEC 60309 2P+NE, 32 A receptacle.

In various embodiments described above, a feed system is wired toprovide any combination of phases from a three-phase power source. Afeed system may, however, provide other types of power (for example,two-phase, single phase). In one embodiment, a secondary feed systemreceives two-phase power from a power source and allows synchronizationfor any combination of phases of the two-phase power. In one embodiment,a secondary feed system receives single-phase power (for example, onehot and one neutral) from a power source and allows synchronization withany phase and neutral of a poly-phase system.

In some embodiments, a set of secondary feed lines (for example, backfeed lines) and a set of input lines may be tested to determine a matchbetween a pair of lines in the set of secondary feed lines and the setof input lines on a primary power system. Determining the match mayinclude matching the phase of the pair of secondary feed lines with thephase of the pair of input lines. The pair of secondary feed lines maybe coupled to the matching pair of input lines while primary power ismaintained to the systems. In certain embodiments, a synchronizationsystem is used to test lines of the feed cable and lines of an inputcable to establish a match of phase and polarity between a pair of linesin the set of feed lines and a pair of lines in the set of input lines.U.S. patent Ser. No. 12/892,750, “Method and System for Establishing aPower Feed to Systems During Operation”, filed Sep. 28, 2010, which isincorporated by reference as if fully set forth herein, includessystems, devices, and techniques that may be used in various embodimentsto establish power feeds and to maintain and reconfigure computingsystems.

In various embodiments described above, a secondary feed is establishedfor systems during operation of the systems. In certain embodiments,however, some or all of the systems in a data center may be taken out ofoperation during establishment of a secondary feed.

Although in some embodiments described herein, an additional feed is asecondary feed connected in parallel to a single primary feed, powerfeeds may, in various embodiments, be added to systems having any numberof existing feeds. Thus, an additional power feed may be a secondarypower feed, a tertiary power feed (for example, a feed to a systemreceiving power from two existing power systems), etc.

The various methods as illustrated in the Figures and described hereinrepresent exemplary embodiments of methods. The methods may beimplemented in software, hardware, or a combination thereof. The orderof method may be changed, and various elements may be added, reordered,combined, omitted, modified, etc.

Although the embodiments above have been described in considerabledetail, numerous variations and modifications will become apparent tothose skilled in the art once the above disclosure is fully appreciated.It is intended that the following claims be interpreted to embrace allsuch variations and modifications.

What is claimed is:
 1. A system, comprising: a primary power source foran electrical load that includes a residual current device; a donorpower source for the electrical load that does not include a residualcurrent device; a secondary feed system comprising: a set of secondaryfeed lines configured to supply power from the donor power source to theelectrical load; a splitter device configured to split power from thedonor power source; and a feed-switching device configured to switchpower through one or more of the secondary feed lines; and an automatictransfer switch (ATS) configured to couple in parallel with thesecondary feed lines, wherein the donor power source is configured tosupply power to a secondary input of the ATS via the splitter device andat least some of the secondary feed lines and the primary power sourceis configured to supply power to a first input of the ATS via one ormore other feed lines, wherein the splitter device is configured toconcurrently: supply a first split portion of power received from thedonor power source to the electrical load via the ATS and an input cableof a power distribution unit coupled to the electrical load; and supplya second split portion of power received from the donor power source tothe electrical load via the feed-switching device and a back feedconnection to an output receptacle of the power distribution unitcoupled to the electrical load.
 2. The system of claim 1, wherein theelectrical load comprises rack-mounted computing devices in a datacenter.
 3. The system of claim 1, wherein the set of secondary feedlines is configured to couple in the output receptacle of the powerdistribution unit.
 4. The system of claim 1, wherein the automatictransfer switch (ATS) comprises an alternate source ATS input, whereinthe splitter device and the alternate source ATS input are configured tobe coupled together via one of the secondary feed lines to supply thesecond split portion of power received from the donor power source tothe electrical load via the alternate source ATS input of the ATS. 5.The system of claim 1, further comprising a reserve power source for theelectrical load, wherein the reserve power source is configured tocouple with the automatic transfer switch, after the automatic transferswitch is decoupled from the secondary feed lines.
 6. The system ofclaim 5, wherein the donor power source is configured to feed electricalpower to the electrical loads via a separate power output deviceseparate from power output devices via which the primary power sourceand the reserve power source are configured to feed electrical power. 7.A data center comprising: a power distribution unit (PDU) comprising aplurality of power output devices, wherein a first power output deviceof the PDU comprises a residual current device and a second power outputdevice of the PDU does not include a residual current device, wherein aresidual current device is a device configured to trip as a result of animbalance between lines connected to a power output device, wherein thePDU is configured to receive multi-phase power; another powerdistribution unit (PDU) electrically coupled to the first power outputdevice of the PDU that comprises a residual current device; electricalloads electrically coupled to the other PDU; wherein the PDU isconfigured to feed electrical power to the electrical loads via thefirst power distribution device of the PDU electrically coupled with theother PDU; and a backfeed unit configured to electrically couple withthe second power output device of the PDU that does not include aresidual current device and electrically couple with the other PDU whilethe other PDU is feeding electrical power to the electrical loads,wherein the backfeed unit is configured to feed electrical power fromthe second power output device of the PDU to the electrical loads viathe other PDU, and wherein the backfeed unit is configured tosynchronize a phase of power to be fed to the electrical loads from thebackfeed unit with a phase of power currently being fed to theelectrical loads via the other PDU.
 8. The data center of claim 7,wherein the electrical loads comprise computing devices mounted in arack, and wherein the other PDU is a rack PDU associated with the rackin which the computing devices are mounted.
 9. The data center of claim8, wherein the PDU is a floor PDU configured to feed electrical power tothe computing devices mounted in the rack via the first powerdistribution device of the floor PDU and via the rack PDU, and whereinthe floor PDU is configured to feed electrical power to other computingdevices mounted in other racks via other ones of the power distributiondevices of the floor PDU.
 10. The data center of claim 7, furthercomprising an automatic transfer switch (ATS) coupled with the otherPDU, wherein the backfeed unit is configured to electrically couple withthe second power output device of the PDU and electrically couple withthe ATS, via a set of secondary feed lines, to concurrently feedelectrical power from the PDU to the electrical loads via the ATS andthe other PDU.
 11. The data center of claim 10, further comprising asplitter device coupled to the set of secondary feed lines, wherein thesplitter device is configured to electrically couple with the secondpower distribution device of the PDU at an inlet of the splitter deviceand configured to electrically couple via a first outlet of the splitterdevice with the ATS and electrically couple via a second outlet of thesplitter device with the other PDU, wherein the splitter device isconfigured to feed electrical power from the inlet of the splitterdevice to the first outlet and the second outlet of the splitter device.12. The data center of claim 11, further comprising a reserve powersource, wherein the reserve power source is coupled to the ATS via analternate source input cable of the ATS.
 13. The data center of claim 12wherein reserve power source comprises a residual current device.
 14. Asystem comprising: a power panel comprising a first power output devicethat comprises a residual current device and a second power outputdevice that does not include a residual current device, wherein aresidual current device is a device configured to trip as a result of animbalance between lines connected to a power output device, wherein thepower panel is configured to receive multi-phase power; and a backfeedunit configured to couple with the second power output device of thepower panel and couple with a power distribution unit (PDU) that feedselectrical power to electrical loads, wherein the backfeed unit isconfigured to couple with the PDU while the PDU receives electricalpower from the first power output device of the power panel, and whereinthe backfeed unit is configured to synchronize a phase of power to befed to the electrical loads from the backfeed unit with a phase of powercurrently being fed to the electrical loads via the PDU.
 15. The systemof claim 14, wherein the backfeed unit is configured to flow electricalpower to the electrical loads when the backfeed unit is coupled with thePDU and continue to flow electrical power to the electrical loads aftera flow of power via the first power output device is interrupted. 16.The system of claim 14 further comprising an automatic transfer switch(ATS) coupled to the PDU.
 17. The system of claim 16, wherein: the firstpower output device of the power panel is coupled with the ATS, areserve power source is coupled with the ATS, and an outlet of the ATSis coupled with the PDU.